This is literally what it says in the title.Whenever I click the report to a moderator/admin a message comes up saying I am unable to report post hack. Any assistance on the matter would be greatly appreciated.

Ah okay, you don't have an issue going on and you can still report posts.

It means the post you are trying to report has already been reported. I imagine it is from that one troll, to my knowledge every post of theirs has been reported so no one can report them further. This is so that mods don't get flooded with reports pointing them to the exact same post. I hope that clears it up.